1. Field of the Invention
The present invention relates generally to a gas turbine engine, and more specifically to an air-cooled turbine rotor blade with a serpentine flow cooling circuit.
2. Description of the Related Art Including Information Disclosed Under 37 CFR 1.97 and 1.98
In a gas turbine engine, a high temperature gas flow is passed through the turbine to produce mechanical work to drive the compressor and, in an industrial gas turbine engine, to also drive an electric generator and produce electrical energy. Passing a higher temperature gas flow into the turbine can increase the efficiency of the engine. However, the turbine inlet temperature is limited by the material properties of the first stage stator vanes and rotor blades as well as the amount of cooling that can be produced by passing cooling air through these airfoils (vanes and blades). Airfoil designers try to minimize the amount of cooling air used in the airfoils since the cooling air is typically bled off from the compressor and thus is not used to produce work and the energy used to compress the air is thus wasted.
FIGS. 1 and 2 show a prior art turbine rotor blade with a triple pass serpentine flow cooling circuit design. The serpentine flow circuit is used in order to lengthen the flow path through the airfoil. However, for a blade with a single cooling flow circuit, cooling air is supplied through the blade leading edge flow channel with a leading edge showerhead design while a majority of the cooling air is discharged through the blade trailing edge. A blade cooling of the FIG. 1 design requires a high cooling air supply pressure to fulfill the blade leading edge showerhead back flow margin (BFM) where the internal pressure is higher than the external blade pressure to prevent the hot gas from flowing into the blade cooling circuit and the second leg down pass out flow margin (OFM) requirements. In addition, high cooling supply pressure will normally cause a high-pressure ratio across the blade trailing edge. The high pressure ratio across the blade trailing edge will yield small cooling features which decrease the casting yield and increase the variation of cooling flow. An alternative way to provide an effective cooling design arrangement for a low cooling flow design with high cooling supply pressure of a single triple pass serpentine blade is to use multiple compartment cavities and backside impingement with a single impingement metering hole to control the serpentine internal pressure distribution.